You should be using a 50/50 blend of water and coolant year 'round. The coolant has additives that not only prevent freezing and raise the boiling point, but provide rust protection and lubrication. Porsche recommends its own (expensive) brand of coolant. However, any good brand such as Prestone, will do. And, leaving the system dry is not a good idea.

Also it is OK to drain and leave it dry if you suspect freezing temps (i.e. the power goes out). We had to drain every night when running the (late) Grand Targhee hillclimb at 7851 ft. Just refilled in the morning with jugs from the room and you are on your way.

I change it every 2-3 years to replenish the additives in the water wetter because the water wetter gets slowly diluted over time as I top up using only distilled water.

Water alone is a better conductor of heat (+17% heat capacity at 220F as compared to 50/50 antifreeze). Plus, in the case of a leak/incident, water + water wetter doesn't create an oily slick on the track like antifreeze.

My indie and chief PCA instructor here in AZ recommended distilled water and water wetter. I initially disagreed with him about the reduced boiling temp compared to 50/50 mix but it is true that it extracts heat better. I think that the coolant system pressure elevates the boiling point of water so 220F is fine. I live in AZ so it doesn't affect me too much. Also what THSTONE said about loosing coolant on the track... that makes sense to me if you track your car a lot. I do wonder however about the anti corrosion properties of the antifreeze...

...Plus, in the case of a leak/incident, water + water wetter doesn't create an oily slick on the track like antifreeze.

Exactly. Point in case... this recent Nürburgring 14 car pileup. Unfortunately, cause was preventable two ways... first running WW as opposed to coolant. More importantly someone did not fix the well documented coolant hose pop-off issue of 996/997 Turbo, GT3, GT2 and GT3RS... First hand saw a similar incident a few years ago at Mid-O when a 996's popped in Madness... 8-9 cars collected quickly against tirewall before corner worker could flag traffic.

P-car and other carnage not for faint of heart... Thankfully the injuries limited from what I've read:

LIFESAVING lesson E30 driver ignored was 'unless you/your car are on fire... stay IN your vehicle until safety personnel are on scene and advise you to exit'. He was EXTREMELY lucky on a number fronts... Not to mention the driver who stayed on track side of armco

All OEM coolant, in spite of "lifetime" monikers need changed. In most cases though "lifetime" means until some other part's lifetime ends resulting in dumping much of your coolant; at which point you have to replace

WW will break down w/ extensive & extreme hi-temp exposure (google can help you find their MSDS and ASTM spec info).

All in all though, you're not going to find a "frequency guide" b/c too much depends on how and under what conditions you use your car... same w/ oil changes and brake bleeding/flushing. In most cases those minimally are annual and every two or three years respectively (usage dependent).

Personally, I err on side of caution and change more frequently than not. You know, I've never had a motor (or service adviser for that matter) complain about too frequent oil change. Well one time a BMW SA did but that's another story... And, in the grand scheme of things it's VERY inexpensive for the cheap insurance provided.

Using Tom's schedule (which I have used in many cars, again with no ill effect ), on the second year the mix tends to discolor. Does this mean something is awry, probably not.

My M3 has a cast iron block and the coolant looks cloudy and brown after a few months.The boxster stays clean with a red/pink hue on the yearly scheme and my interval is mostly based on taking something apart that needs the coolant drained.

For track cars, run water and a supplement of whatever brand you find handy. Straight H20 works too.

Having the system dry is fine but don't start the car! It's all too easy to do on extended projects ( I put warning post-its everywhere now)

Distilled plus water wetter works fine and the only downside I can see is losing some of the corrosion protection from OEM coolant that protects your T-stat, water pump, and internals. All coolant should be changed periodically as it does get contaminated over time. Following thstone's schedule makes sense to me.